In relation to a wireless communication system, an application of network-coding to a wireless repeater (RS: Repeater Station, hereinafter abbreviated as “RS”) has hitherto been discussed.
An RS has a function of relaying data transmitted from a mobile station (MS: Mobile Station, hereinafter abbreviated as an “MS”) to a base station (BS: Base Station, hereinafter abbreviated as a “BS”) and relaying data received by the BS to the MS. Meanwhile, network-coding is a technique for enabling a performance of efficient relaying by subjecting relay data to coding at a relay node.
FIG. 1 shows an example application of network-coding to an RS. An example application of network-coding to an RS is specifically described by use of FIG. 1. In FIG. 1, reference symbol RS is assumed to relay data S1 transmitted from an MS to a BS or relay data S2 transmitted from the BS to the MS. After the RS conducts a relaying operation by subjecting the data S1 and S2 to network-coding and simultaneously transmitting the data S1 and S2 to the MS and the BS by the same channel (the same resource).
Network-coding effected by the RS is now described. The RS subjects a bit sequence of the data S1 and a bit sequence of the data S2 to XOR (Exclusive OR) operation. In the example shown in FIG. 1, since S1=“1111” and S2=“1010” are achieved, an XOR result comes to “0101.” The XOR result “0101” is simultaneously transmitted to the MS and the BS.
Receiving operation of the MS and the BS is now described. The MS performs XOR operation between the XOR result “0101” transmitted from the RS and the data S1 “1111” transmitted by the MS, whereby extraction of the data S2 “1010” transmitted from the BS becomes possible. Likewise, the BS performs XOR operation between the XOR result “0101” transmitted from the RS and the data S2 “1010” transmitted from the BS, whereby extraction of the data S1 “1111” transmitted from the MS becomes possible.
FIG. 2 is a descriptive view of network-coding to which a plurality of packets are to be subjected. After received the plurality of packets (S1 to S6) from the MS and the BS, the RS broadcasts the packets by one operation through use of network-coding. A resource used for network-coding is determined by amounts of data from the MS and the BS and channel quality.
FIG. 3 shows example network-coding performed when the amount of data varies from one destination (an MS or a BS) to another destination. As shown in FIG. 3, when data to be transmitted to the MS and the BS differ from each other in terms of an amount, the RS subjects data to network-coding after matching a smaller data size to a larger data size. A conceivable method for matching a data size is, for instance, 0-padding.
FIG. 4 is a view for describing another related art technique. When failed to receive a data packet from the MS or the BS, the RS solely performs transmission by use of a resource for network-coding without performance of network-coding (e.g., see Patent Document 1).
Patent Document 1: US2007/0081603A